a —————— 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 43 
as to operation, size of plant, costs and other matters, Ormandy’s 
article and the interesting discussion on the part of members of the 
Ceramic Society should be consulted. 
Among the advantages claimed for the method are (1) greater ease 
and steadiness of operation; (2) smaller plant-space ; (3). lower 
labour cost; (4) process not only dewaters clay but purifies it aa 
well, thus supplementing the preliminary settling treatment, (5) clay 
after treatment is very plastic'/and sinters ata temperature far below 
the melting point.”! 
Schwerin’s “osmose” method has been discussed critically by 
Bleininger2 who points out that the “osmose ” machine is merely 
a substitute for the filter press or centrifuge, having the advantage 
over most filter apparatus of being automatic and continuous. By 
experiments of his own Bleininger assured himself that no measur- 
able purification occurred during the cataphoretic separation of the 
clay ani that such change as the clay finally underwent was due to 
the preliminary deflocculation and settling. At the present time 
Bleininger” is of the opinion that, although the “ osmose”’ process 
can be made to work satisfactorily, the same results can be obtained 
without the use of the electric current by deflocculating the clay 
with caustic soda, thus removing the granular impurities, coagulating 
the suspension with acids or aluminum chloride and filtering out 
the precipitated material. At any rate no electro-osmose plants are 
in operation in the United States, while the precipitation process is 
giving satisfaction at the Saylersburg, Pa. plant of the Miner-Edgar 
Company, Brooklyn, N.Y., and that of the Georgia Kaolin Co,, at 
Macon, Georgia. 
There seems to be a great deal of misunderstanding with regard 
to the extent to which the “osmose” machine acts as a purifier. 
Ormandy points out that clay or kaolin particles are electro-negative, 
silica is more or less neutral while oxides of iron and titanium are 
positive. Hence only kaolin migrates to the anode, silica settles out 
and the iron collects at the cathode. In the first place, suspended 
ferric oxide, although called a positive colloid, is not necessarily 
positive against an alkaline soluticn and probably is electro- 
negative*t unless there happens to be present in the solution some 
strongly adsorbed cation, such as calcium or magnesium, to counter- 
act the effects of hydroxyl. Another point which has been over- 
looked is the condition of the iron oxide in the clay—if the oxide is 
adsorbed by the kaolin the electrical treatment cannot remove an 
appreciable amount of iron from the clay. To be sure, Schwerin” 
claims that adsorption compounds can be broken up by electrical 
endosmose or catapboresis, but this can occur only when there is a 
relatively large amount of one substance in the liquid phase and in 
adsorption equilibrium with the solid phase. As to the results 
actually obtained, it is interesting to note that of 25 clays reported 
21 Of. Brit. Pat. 3434 (1913). 
22 Trans. Am. Cer. Soc. 15, 338 (1913); Zechn. Paper U.S. Bur. Standards 51, 
1915). 
; 38 ae communication to the author, June, 1918. 
% Ferric oxide peptized by glycerine and NaOH is negative and migrates to the 
snode. Fischer and Kusnitzky : Biochem Zeit., 27, 311 (1910). 
25 Brit. Pats. 14369 (1912). 
